Walking is the most commonplace of activities, yet we know remarkably little about it and no robot has yet reproduced the grace and poise of a human walk. Steven Collins et al. now show that the attachment of a simple mechanical exoskeleton to the foot and ankle results in a 7 reduction of the metabolic energy expended in walking. This work shows that net energy input is not a fundamental requirement for reducing the metabolic cost of human walking, and that reducing calf muscle forces while also fulfilling normal ankle functions and minimizing penalties associated with added mass or restricted motions can be beneficial
